Microscopy Solutions for Virology

In clinical routine a multitude of laboratory methods are available to  confirm virus infections. With the advent of molecular techniques and increased sensitivity of serological assays, virology has changed rapidly with a wide variety of samples used for virologic testing.

Many viruses can be grown in cell culture in the lab. To do this, the virologist mixes the virus sample with suitable host cells, a process called adsorption or inoculation, after which the cells become infected and produce more copies of the virus. Although some viruses require a certain type of cells for replication, there are cells that support growth of a large variety of viruses such as the African monkey kidney cell line (Vero cells), human lung fibroblasts (MRC-5), and human epidermoid carcinoma cells (HEp-2).

One sign of knowing whether the cells are successfully replicating the virus is to  search for changes in cell morphology or  for  increased cell death  (apoptosis) using an inverted microscope for cell culture applications. These induced morphological changes are referred to as cytopathic effect (CPE). Light microscopy is also a valuable tool to quickly and efficiently  observe histopathological changes  such as typical aggregates of virus inside cells in so-called cytoplasmic inclusion bodies. One prominent example are the Negri bodies that are larger pathognomonic cellular inclusions typically observed with an hematoxylin and eosin stain (HE stain) in various nerve cells to detect rabies infections with the lyssavirus.

Fluorescence microscopy becomes increasingly important in virology.  Immunofluorescence  is one method of diagnosing and quantifying certain viral infections. The advancement of fluorescence labeling methods and microscopic instrumentation opens further possibilities to perform more refined studies on host-virus interactions, virus spreading, and virus replication, e.g. through co-localization measurements between cellular compartments and virus. Increased sensitivity, better resolution, and higher automation of those microscope systems provide the basis for screening applications that allow researchers to  get a wealth of information on virus infected cells, e.g. upon drug treatment.

Electron microscopy  is often used to examine the ultrastructure and to identify certain viruses. In particular, the correlation between light and electron microscopy (CLEM)  can provide unique insights  into the interactions between virus and host.

For observation and maintenance purposes in cell culture, inverted light microscopes with a small footprint, LED fluorescence option, good ergonomics and high-quality optics for  reliable digital documentation  are essential tools. Immunofluorescence opens up the rapid detection of viral agents with direct (DFA) or indirect fluorescence antibody (IFA) tests, including antibody test kits against herpes simplex (HSV), Influenza A, other respiratory viruses and enteroviruses.

Automated boxed microscopes  with integrated calibration, environmental control and fluorescence options are  ideal for lab  environments  with high throughput  demands, enabling fully automated 2D and 3D screening of cell cultures and tissues. Confocal microscopes give the virologist the option to investigate the details of cellular invasion in  greater detail  and prepare the respective sample for further investigation with immune electron microscopy.

Recent developments in scanning electron microscopy (SEM) have shown to meet the resolution and image quality requirements for virus studies. The large field of view imaging mode in combination with correlative light microscopy and automated workflows  saves valuable time  in finding relevant viral spots and provides  fast results, even in 3D.